System and method for industrial scale continuous holographic lithography

ABSTRACT

A system and method for patterning of a substrate at sub-micron length scales using interference lithography that includes a substrate; a chuck that promotes substrate motion; at least two EM beams; a beam phase controller, wherein the phase controller modifies phases of the EM beams with respect to each other creating an interference pattern; a displacement sensor that measures the substrate displacement; and a feedback control mechanism configured to monitor and synchronize the substrate motion with the interference pattern using the beam phase controller and the displacement sensor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. patentapplication Ser. No. 15/980,362, filed on 15 May 2018, which claims thebenefit of U.S. Provisional Application No. 62/506,442, filed on 15 May2017, both of which are incorporated in their entireties by thisreference.

TECHNICAL FIELD

This invention relates generally to the field of holographiclithography, more specifically to a new and useful system and method forhigh throughput, industrial scale continuous holographic lithography.

BACKGROUND

Holographic lithography (also referred to as interference lithography)is a technique for patterning regular arrays of fine features, withoutthe use of complex optical systems and photomasks. In holographiclithography an interference pattern is generated between two or morecoherent light waves and transferred to a typically photosensitivematerial (e.g. photoresist). The interference pattern comprises aperiodic series of intensity minima and maxima created by constructiveand destructive interference of the light waves. The period of thespacing for two light waves is given by (λ/2)/sin(θ/2), where λ is thelight wavelength and θ is the angle between the two interfering waves.Using this pattern, a 3-beam interference pattern may be used togenerate patterns with 2D symmetry, and 4-beam interference patterns maygenerate patterns with 3D symmetry.

To create precise interfering patterns, beam coherence is important.Using broad bands of light create “smearing” effects of the interferencepattern. For this reason, monochromatic light is typically used inholographic lithography. The band width of a light beam is typicallynarrowed using diffraction gratings and beam splitters that diffract atdifferent angles for different wavelengths and thereby dissipatingunwanted wavelengths. Often holographic lithography may be used as aninitial step to create a master structures for subsequent microprocesses. Holographic lithography is used to create and modify metals,ceramics, and polymers, and is commonly used in the fields ofphotovoltaics and biotechnology. FIG. 2 shows an example of conventionalholographic lithography in which the photomaterial is stationary. Aphotoresist-coated substrate S is rigidly attached to chuck C. GratingsG splits the input beam B, the results of which are directed by mirrorsM to interfere at the substrate, forming latent image LI. Half- andquarter-wave plates (HW, QW) set the beam polarizations while theneutral density filter ND sets the relative amplitude of the centralbeam. As seen in the figure, the substrate is fixed in place.

A photoresist is a light sensitive material used in many processes totransfer patterned coatings to a surface. A photoresist is created bycoating a substrate with a light-sensitive material (typically organic).A patterned mask may additionally be applied onto the surface of thephotoresist to protect regions of the substrate that should not beexposed to light. The photo is then exposed to light, wherein theregions exposed to light are washed away leaving only the masked areasbehind. Alternatively negative photoresist substrates also exist,wherein the regions exposed to light become cross-linked and harden. Asolvent is then used to wash away the regions that were masked. Examplesof possible photoresist materials include tbutoxycarbonyl (t-BOC),methyl methacrylate, diazonaphthaquinone (DQ), and diazonaphtoquinone(DNQ). Photoresists are most commonly sensitive in the ultraviolet (<450nm) spectrum but alternate photoresists with lower or highersensitivities do exist.

A drawback of interference lithography is that it is limited topatterning arrayed features uniformly, making it difficult to createcomplex and arbitrary shapes. Masking of the substrate (i.e.covering/coating the substrate with a light protective layer) can aid inthis process, but still inhibit the production of complex structures.Current technologies lack the combination of fine control and speed toproduce three-dimensional nanostructured materials in a cost-effectivemanner and/or at scale.

Another drawback of current interference lithography is the inability topattern large substrates with continuous patterning. Moving either thesubstrate or the interference pattern typically leads to smearing out ofthe interference pattern. Current technologies have not developed adynamic method for implementing holographic lightography.

Thus, there is a need in the holographic lithography field to create anew and useful system and method for high throughput, industrial scalecontinuous patterning holographic lithography. This invention providessuch a new and useful system and method.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic representation of a system of a preferredembodiment;

FIG. 2 is an exemplary representation of one conventional stationaryholographic lithography embodiment;

FIG. 3 is an exemplary representation of one embodiment (front view) ofthe system, common to some active, passive, and hybrid phase controlmethods;

FIG. 4 is an exemplary representation of one embodiment of the systemusing passive phase control;

FIG. 5 is an exemplary representation of one embodiment of the systemusing active phase control;

FIG. 6 is an exemplary representation of a preferred picture embodimentof the system; and

FIG. 7 is a flowchart representation of a method of preferredembodiment.

DESCRIPTION OF THE EMBODIMENTS

The following description of the embodiments of the invention is notintended to limit the invention to these embodiments but rather toenable a person skilled in the art to make and use this invention.

1. Overview

A system and method for the application of holographic lithography of apreferred embodiment functions to enable three-dimensional (3D)holographic lithography, more specifically continuous holographiclithography, at an industrial scale. The system and method preferablyenable continuous patterning of a substrate in one, two, or threespatial dimensions at a sub-micron scale. In particular, the system andmethod is preferably used in connection with holographic nanolithographybut may alternatively be used with holographic lithography approaches toenable patterning at larger scales such as at scales of tens to hundredsof microns. Four or more optical beams overlapping may create athree-dimensional interference pattern in a photosensitive material,herein referred to as a photomaterial. The photomaterial may be aphotoresist or other substance which changes properties in response toelectromagnetic (EM) radiation. The photomaterial may be coated onto asubstrate attached to a moving chuck or processed in a continuous formatsuch as roll to roll.

The phase (or other property) of one or more of the optical beams iscoordinated with the motion of the photomaterial so that the resultinginterference pattern is motion-synchronized with the photomaterial andproduces a sharp, high contrast latent image. Herein, motionsynchronized characterizes object state coordinated with motion of thephotomaterial as a form of cooperative motion. Control of theinterference can be motion-synchronized. Additionally position of amirror can be motion-synchronized as may be used in a passive variationas described herein. Subsequent processing develops the latent imageinto a three-dimensional morphology. It should be noted that a minimumof two or three noncoplanar beams can be used to create one- ortwo-dimensional structures, respectively.

Coordination of the optical phase control with the moving photomaterialto the accuracy required for making continuous features is a majordifficulty for the problem confronted here, particularly at the micronand sub-micron levels. Even small differences between the velocity ofthe photomaterial and interference pattern can smear out the latentimage. The system and method employ phase control methods to solve thissynchronization problem. A passive method which “auto-synchronizes”, anactive method which consists of dynamically modifying the phase tomaintain synchronization, and a combined hybrid of the passive andactive method may each be used to overcome the synchronization problembetween the optical phase control and the motion of the photomaterialsubstrate.

All three phase control methods function to create a moving interferencepattern. The active, passive, and hybrid methods have variousadvantages. The passive approach has an advantage of relative simplicityand the potential for self synchronizing or automatic alignment in someembodiments. The active approach has an advantage of increasedprogrammability and easier scalability. The hybrid approach incorporatesadvantages of both the active and passive methods. It should be notedthat the system and method are capable of altering the phases,amplitudes, wave vectors, coherence, and/or polarizations of the opticalbeams dynamically. This can be accomplished by using optical modulators,wherein the system may include one or more optical modulators acting onone or more EM beams. A sequence of optical modulators or any suitableconfigured optical system may act on one or more EM beams. The opticalmodulators can preferably be dynamically controlled using the activeapproach, a passive approach, and/or a hybrid approach. For example, thesystem may additionally include a polarization and/or amplitude opticalmodulator. Alternatively, a single optical modulator may be used inaltering a set of optical properties. Note modulators can operate ondifferent principles, for example electro-optic, acousto-optic, oranother suitable mechanism. Modulators can act on more than one beam.Multiple modulators with different principles of operation for alteringphase or other beam properties can be used. Beams can also be modulatedby scattering from a mask, other mirror, or diffraction grating whichcould be mounted to the chuck or on another mechanical actuator.

The system and method may afford many advantages over currently usedholographic lithography techniques. Structures of high precision may becreated efficiently and in large scale. Dependent on substrate materialand thus interference pattern wavelength, substrate units of at least150 nm long may be patterned. When patterning a substrate into porousstructures, pore sizes of at least 10 nm (to approximately 120 nm) canbe generated within the substrate (with the practical maximum limitbeing approximately 80% of the subunit length, and the minimum subunitlength is λ/2). The phase of the optical beams may be adjusted in realtime, making the interference pattern motion-synchronized and allowingfor a high level of precision in pattern formation upon the substrate.With continuous motion of the substrate, the system and method allow foran industrial scale modification of substrate units that has not beenpreviously available in today's market.

As another potential benefit, the continuity of the patterning may givethe invention an advantage over conventional projection, contact,proximity, interference, and holographic lithography, which are serialtechniques. Continuous patterning with conventional methods requires anoverlapping series of discrete or scanning beam exposures using multiplepasses, which are difficult to implement. For example photolithographycurrently requires 50 passes to create a CMOS integrated circuit. Thesystem and method can enable continuous patterning of arbitrary lengthsof a photomaterial.

As another potential benefit, the system and method may additionallyenable formation of gradient patterns into the substrate using a spatiallight phase modulator. The system and method further allow the use ofmultiple optical beams at different wavelengths. Both multiple beams andmultiple continuous passes enable the invention to potentially generatemore complex patterns at sub-micron levels of precision with greaterefficiency. A general weakness of holographic lithography has been thelack of ability to generate complex patterns. Complex structures mayserve advantages in the field of semi-conductors and building of MEMSthat is a region where until currently holographic lithography has notbeen employed. Additionally, the construction of porous structures mayhave application in the design and construction of chromatographyfilters.

As another potential benefit, the method may be faster and simpler thanconventional lithographic methods that create three-dimensionalstructures layer by layer. These methods operate by building up athree-dimensional structure out of layers that have essentially one ortwo-dimensional structure. The method also avoids the problems ofalignment with which layer by layer approaches must contend. Photoniccrystals have application in thin-film optics of lenses and in opticalcomputers and are currently built in this layering fashion. Thusphotonic crystals may be generated more efficiently and with fewerdefects as compared to current methods.

As another potential benefit, the invention does not require a mask(though some embodiments could incorporate one), which is an advantageover many conventional lithographic techniques that do. These includeconventional photolithography, nanoimprint lithography, and rolling masklithography. Methods dependent on masks need a new mask to be made foreach new pattern or material structure that is developed. Developing amask at sub-micron scales has its own difficulties, while generating anappropriate interference pattern can be done very precisely usingcomputers to generate the proper theoretical interference pattern andthen employing these patterns with precise and coherent lasers.

As another potential benefit, the system and method allow for creationof structures with sharp features or smoother features using real timephase adjustment. By changing the phase modulation in small increments,the sharp contrast of the interference pattern may be smoothed outcreating more curved (as opposed to sharp edged) patterns. Smooth shapesmay be useful in the field of optics, and aid in creating precisesub-micron lenses at an industrial scale.

2. System

As shown in FIG. 1, a system for patterning of a substrate at sub-micronlength scales using interference lithography, of a preferred embodiment,can include a substrate 100; a chuck 200 that may promote substratemotion; at least two EM beams 300; a beam phase controller 400, that mayalter the phase difference between the at least two EM beams creating aninterference pattern; a displacement sensor 500, that measures thesubstrate displacement; and a feedback control mechanism 600, thatmonitors and synchronizes the interference pattern with respect to thesubstrate motion, using the beam phase controller 400 and thedisplacement sensor 500. The system functions to create a pattern on orinto the substrate 100. The system may be customized to create patternsin multiple dimensions (i.e. 1D, 2D, or 3D) and create patterns ofdiffering complexity (e.g. periodic patterns, gradients, or arbitrarypatterns).

The substrate 100 of a preferred embodiment functions as the material tobe modified. The substrate may be thin enough such that light canpenetrate completely through (e.g. typically a maximum thickness ofapproximately 1 mm). In a preferred example, the substrate 100 is apositive photosensitive material such that Electromagnetic (EM) beams300 of, or near, a particular wavelength will degrade the material. Thesubstrate 100 may alternatively be composed of a negative photosensitivematerial (i.e. light reinforces the substrate) or not photosensitive atall. In some preferred implementations the photosensitive substrate 100may be a photoresist such as a base substrate coated withlight-sensitive organic material. Light exposure causes a photochemicalreaction which changes the solubility of the photoresist in response tolight absorption, thereby generating a latent image. For example, in anegative photoresist, such as SU-8, light absorption leads to crosslinked regions which remain upon immersion in developer. Post-exposureprocessing, including postbaking and development, reveals thethree-dimensional polymer nanostructure. The photoresist substrate 100may thereby be “patterned” by exposing the substrate 100 to aninterference pattern created by EM beams 300 of the appropriatewavelength. Alternatively, for a non-photosensitive substrate 100, theEM beams 300 may be used to etch out a shape into the substrate 100.

In some examples the substrate 100 may be photosensitive at multiplewavelengths. Photosensitivity may be either positive, negative, or anycombination of the two. Photosensitivity at multiple wavelengths mayallow the substrate 100 to be patterned using multiple interferencepatterns simultaneously (in the case of positive sensitivity) or allowfor higher precision of patterning by protecting certain areas of thesubstrate 100 while patterning adjacent areas of the substrate 100 (e.g.by protecting regions of the substrate 100 by exposing the substrate 100to the negative sensitive wavelength adjacent to the positive sensitivewavelength interference pattern).

A more comprehensive material palette can be exploited by using thepatterned photoresist substrate 100 as a template. Methods such aselectroplating or chemical vapor deposition can be used to deposit othermaterials into the defined void space (i.e., patterned cavity) of thepatterned photoresist which can then be removed. In this way thesubstrate 100 can be used as mold, template, or scaffold. Thephotoresist can be removed after the deposition of other materials, forexample by etching, burning, or possibly evaporation. Alternatively, thesubstrate 100 could instead be a functional photo-material. Thismaterial remains after development and forms a functional part of thestructure. Further deposition of other materials in and onto the alreadyfunctional structure is also possible.

In some variations, the substrate 100 could be a non-solid substratesuch as a photosensitive fluid or gas in which light exposure causesmaterial deposition or hardening. That is EM radiation may cause eithermaterial to collect into a specific pattern on or within the substrate100, or the substrate itself may undergo a phase transition and solidifyinto a specific pattern.

The chuck 200 of a preferred embodiment functions as a stabilizer andactuator for the substrate 100. The chuck 200 preferably uses a suitableactuator system that functions to promote chuck actuation in one or moredimensions. Chuck actuation may enable the substrate to be modifiedduring motion, allowing for long continuous modification of a singlesubstrate, allowing high through put assembly line type substratemodifications to a single substrate traveling through multiplemodification areas in series, and/or allowing for a line of substratesubunits to be modified in rapid succession.

The substrate 100 may preferably be rigidly attached to the chuck 200and move with the chuck actuation. Chuck actuation may occur fromnanometer to micron length scales. Alternatively chuck actuation mayoccur at other length scales. Chuck actuation may be at a constant rate,or may vary as necessary. Chuck 200 motion is preferably automated andcontrolled from an external interface. The actuating motion of the chuck200 may be in 1, 2, or 3 dimensions. The actuating motion may betranslational, rotational, or any other combination of motion.

The chuck 200 may additionally provide stability to the substrate 100.The chuck 200 may help provide a strong rigid structure to hold thesubstrate 100 fast with minimal external effects. The chuck itself maybe made of very sturdy material such that fluctuations due to thermaland vibrational energies within the chuck 200 may be much less than thesub-micron rate of motion of the chuck.

The electromagnetic (EM) beams 300 of a preferred embodiment function togenerate the pattern that is then transferred upon the substrate. The EMbeams 300 may directly create the pattern upon the substrate byradiating particles upon the substrate, but may alternatively cause achange to the photoresist substrate 100 to change solubility. Preferablythe EM beams 300 create an interference pattern around a specificwavelength that creates the pattern upon the substrate. To create aninterference pattern the EM beams 300 need to have relatively close orexactly the same wavelength, thus EM beam 300 coherence is important tocreate the interference pattern. The closer the wavelengths of the EMbeams 300 are, the sharper the interference pattern generated by the EMbeams 300 becomes. Thus alternatively two or more EM beams 300 that arerelatively dissimilar (but close enough to interfere with each other)may be used to create less sharp patterns, “smeared” patterns.

Patterns created upon the substrate may be 1, 2, or 3 dimensional. Tocreate a pattern in 1D, at least two EM beams are required. To create apattern in 2D, at least three EM beams are required. To create a patternin 3D, at least four EM beams are required. That is, a minimum of N+1beams are preferably used to create interference patterns in Ndimensions. Additional EM beams may be used to create more complexstructures and/or to more efficiently pattern the substrate.

The phase controller 400 of a preferred embodiment functions to changethe phase of a subset of the EM beams 300 to generate and control theshape of the interference pattern. As the substrate actuates through theinterference pattern the phase controller 400 may modulate the phase ofthe EM beams to “move” the interference pattern such that theinterference pattern stays fixed with the same interference profile uponthe same location of the substrate 100. That is to say, the peaks andvalleys of the interference profile may stay fixed upon the substrate100 due to the phase controller 400 changing the phase of the subset EMbeams 300 and thus shifting the interference pattern. The phasecontroller 400 may preferably change the phase in real time. The phasecontroller 400 is preferably made up of phase modulators placed alongthe path of the EM beams 300 Examples of phase modulators may include ofelectro-optic, liquid crystal, acousto-optic, or thermal. The phasecontroller 400 may alternatively change the EM beam phase by lengtheningor shortening the distance that the EM beam travels to reach thesubstrate.

The displacement sensor 500 of a preferred embodiment functions tomeasure the chuck 200 movement/displacement during operation, therebymeasuring the substrate 100 movement/displacement and/or velocity (e.g.interferometer). The displacement sensor 500 may be any type of sensorthat can accurately measure nanometer lengths or larger. Thedisplacement sensor may be directly or indirectly connected to thefeedback control mechanism 600. The displacement sensor 500 may beinterferometric type using light, but alternatively could operate viamechanical, inertial, or other mechanism.

The feedback control mechanism 600 of a preferred embodiment functionsto adjust the interference pattern generated by the EM beams 300 suchthat the interference pattern is motion-synchronized with the substrate,enabling continuous and precise patterning of the substrate 100. Thefeedback control mechanism 600 may use information from the displacementsensor 500 to determine the motion of the substrate 100 and may controlthe phase controller 400 to respectively adjust the EM beams' phases tomaintain the motion-synchronized interference pattern. In a preferredvariation a motion-synchronized interference pattern may be maintainedby adjusting the generated electric field of the interference patternsuch that the electric field is moving at the same velocity as thesubstrate actuation. Alternative variations may be used. Maintaining amotion-synchronized electric field is just one variation to maintain amotion-synchronized interference pattern. Other dynamic phase,amplitude, wave vector, coherence, and/or polarization variations may beengineerable to create a moving interference pattern that result in athree-dimensional latent image after exposure. Two implementations ofthe feedback control mechanism 600 (a passive and an active mechanism)will be presented after the underlying mathematical model for thefeedback control is explained.

A mathematical model of the general physics underlying the formation ofthe optical interference pattern and consequent generation of the latentimage highlights key features and limitations of conventionalholographic lithography. For illustrative purposes, the optical beamshere may be approximated as plane waves. The electric field E as afunction of position r and time t is the linear superposition of theseplane waves:

E ( r,t)=Re(A _(m) exp(i[ k _(m) ·r·ωt+ϕ _(m)])),  (1)

where ω is the angular frequency, Re indicates the real part, i is theimaginary unit, and {A_(m),k_(m), ϕ_(m)} denote each plane wave'samplitude vector, wave vector, and phase, respectively (m={1, 2, 3, 4}).The specific absorption rate SAR, which quantifies the exposure processin forming the latent image, is then

SAR( r )=ε_(o)ω Im(n)((½)Σ_(m) A _(m) ·A _(m)+Σ_(m)Σ_((m′≠m)) A _(m) ·A_(m)·cos(( k _(m) −k _(m′))· r +(ϕ_(m)−ϕ_(m′)))),  (2)

where ε_(o) is the permittivity of vacuum, and n is the complexrefractive index of the photomaterial at the frequency of interest(corresponding typically to visible or ultraviolet wavelengths invacuum, though other wavelengths may be used depending on thephotomaterial employed). Judicious choice of the {A _(m), k _(m), ϕ_(m)}allows for periodic structures having any of the 14 Bravais lattices tobe created. (One- and two-dimensional gratings can also be made with twoor three interfering optical beams, respectively.)

Current methods for holographic lithography have critical limitations.Since the interference pattern and hence the specific absorption rateare both stationary, the volume of the nanostructured materials madeduring each exposure is limited by the width of the interfering opticalbeams. A series of exposures can be used to pattern adjacent areas ofphotomaterial, but these patterned areas will in general not becontinuous (there will be stitching errors that must be minimized).

Holographic lithography may be extended for making larger continuouslynanostructured material. Although the interference phenomena describedby (2) can be used to create a wide variety of three dimensionalnanostructures, in practice the volume of patterned material is limited.A means to manufacture continuously patterned nanostructures wider thanthe interfering beams is needed. Suppose the phase ϕm of each planewave, which heretofore was considered constant, instead varies with timeas,

ϕ_(m)(t)=φ_(m)−( k _(m) ·v )t,  (3)

where the φ_(m) are constant and v=vu _(x) is the velocity of thephotomaterial (for example carried by a chuck); the Cartesian unitvectors u _(x),u _(y),u _(z). Then the electric field is

E ( r,t)=Re(A _(m) exp(i[ k _(m)·( r−vt)−ωt+φ _(m)])),  (4)

whose dependence on the quantity (r−vt) indicates continual lateraldrift at the photomaterial velocity. Thus the electric field moveslaterally in synchronization with the chuck and photomaterial. Theinterference pattern and latent image preferably moves laterally insynchronization with the chuck and photomaterial resulting in thedesired latent image. In one example, when,

(1/ω)[Max( k _(m) −v )−Min( k _(m) ·v )]<<1,  (5)

a condition easily satisfied in the laboratory, the SAR is given by

SAR( r,t)=ε_(o)ω Im(n)((½)Σ_(m) A _(m) ·A _(m)+Σ_(m)Σ_((m′≠m)) A _(m) ·A_(m)·cos(( k _(m) −k _(m′))·( r−vt)+(φ_(m)−φ_(m′)))),  (6)

and so the interference pattern too moves laterally in sync with thechuck and photomaterial, thus enabling continuous nanopatterning. Notethat this condition is just one example for certain embodiments of theinvention. Other dynamic phase, amplitude, wave vector, coherence,and/or polarization variations are also possible to create a movinginterference pattern that result in a three-dimensional latent imageafter exposure.

Implementing an additional time-dependent phase shift for one (or more)of the plane waves in (3) such that the interference pattern takes theform (6) or other desired phase control condition is the key requirementfor the feedback control mechanism. Two methods, an active and a passiveapproach, are shown in FIGS. 3, 4, 5, and 6). For illustrative purposes,we consider the fabrication of three-dimensional structures (althoughone- and two-dimensional structures can also be made with variants ofthe described methods). For both methods, four (or more) optical beamsinterfere to produce a three-dimensional interference pattern in thephotomaterial substrate 100 attached to a chuck 200. As shown in FIGS. 4& 5, one of the EM beams 300 may possess a wave vector with a componentparallel to the chuck velocity (k ₁·v≠0). The phase of this beam issynced to the motion of the photomaterial. In one embodiment, the otherthree EM beams are arranged so that their wave vectors lay in the planeperpendicular to the chuck velocity (k _({2,3,4})·v=0); see FIG. 3.These three beams can be created by modifying a single beam using aprism P, beam splitters, or other means. The passive method feedbackcontrol mechanism 600 utilizes reflection from a mirror phase controller400 rigidly attached to the chuck 400, as shown schematically for oneembodiment in FIG. 4. Alternatively the chuck 400 may be converted intoa reflective surface. A substrate 100 is rigidly attached to a movingchuck 200 (or alternatively a substrate rigidly attached to the chuck).An optical EM beam 300 is split by a beam splitter BS. Part of the beamis directed by mirror M5 through a prism P to create three interferingbeams with wave vectors in the y-z plane perpendicular to v, the chuckvelocity in the y-x plane. Another part of the beam is directed bymirror M1 to have wave vector in the x-z plane and interfere with theother three beams in the photomaterial. Another part of the beam isrouted by mirrors M2 and M3 and reflected from mirror M4 rigidlyattached to the chuck, thereby acquiring a varying phase shift. Theangle of the mirror M4 is adjusted so that the optical phase

ϕ₁(t)=φ₁−( k ₁ ·v )t,  (7)

thereby allowing the electric field (4) to be obtained (for the simplecase in which photomaterial is refractive index matched to itssurroundings). This phase control condition is achieved when,

cos θ=2 cos ψ,  (8)

for the configuration and angles defined in the figure. This passivemethod has the advantage of relative simplicity. This method may becapable of varying the motion of the photomaterial during exposure tointroduce programmability into the patterning. That is, the patterningcan be varied based on a design. Note other phase control conditions canbe designed and implemented, for example to compensate for refraction atthe interface between the photomaterial and its surroundings. The mirrorarrangement can be configured such that it is self synchronizing orautomatically aligned. Alternatively, means to implement the passivemethod may take other forms.

The active method is shown schematically for one embodiment in FIG. 5. Asubstrate 100 is rigidly attached to a moving chuck 200. An EM beam 300is split by beam splitter BS. Part of the split beam is directed bymirror M7 through a prism P to create three interfering beams with wavevectors in the y-z plane perpendicular to v, the chuck velocity. Anotherpart of the beam is directed by mirror M6 to have wave vector in the x-zplane and interfere with the other three beams in the photomaterial. Onthe way this part of the EM beam 300 passes through optical phasemodulator OM, thereby acquiring a varying phase shift controlled byfeedback control mechanism 600 with information from displacement sensor500 to satisfy condition (7), or other desired phase control conditiondepending on the configuration, is satisfied. The displacement sensor500 shown in the figure is an interferometric type that measures byreflecting another beam from mirror M8 rigidly attached to the chuck,but alternatively could operate via mechanical, inertial, or othermechanism. The movement of the chuck 200 may be measured via by thedisplacement sensor 500 via interferometry and the phase pi may beadjusted dynamically using an electro-optic modulator or other modulatorto achieve condition (7).

The active method may ultimately achieve more reliable and flexiblephase control with fewer requirements to make critical alignments ascompared to the passive approach, at the cost of a calibration of thephase modulator. Additionally, the method allows the photomaterialmotion to be varied during exposure, in addition to the effects createdby the optical modulators, to introduce programmability into thepatterning. That is, the patterning can be varied based on a design.

The invention can dynamically alter the phases, amplitudes, wavevectors, coherence, and/or polarizations of the optical beams in acontrolled way. This capability can be implemented using the phasecontroller 400 to vary the beams' properties (including spatial lightmodulators); alternatively, the mirror positions and angles could bevaried. Active control also has the advantage that the materialstructure can be programmed during the exposure step. Alternatively,means to implement the active methods may take other forms as listed inthe section on hybrid methods.

FIG. 6 shows one additional embodiment. A photoresist-coated substrate100 is rigidly attached to chuck 200 moving at velocity v. Gratings Gsplit input EM beam 300, the results of which are directed by mirrors Mto interfere at the substrate, forcing latent image LI. Phase modulatorsPM compensate for the chuck movement. Half- and quarter-wave plates (HW,QW) set the beam polarizations while the neutral density filter ND setsthe relative amplitude of the central beam. The inset shows acomputation of the interference pattern.

Note that different arrangements of optical beams are possible thanthose illustrated in the figures. For example, more than one beam canhave a wave vector component parallel to the direction of thephotomaterial velocity. Alternatively, all beams could propagate in theplane perpendicular to the motion of the photomaterial, and the signaldriving the optical modulator in the active or hybrid methods can berapidly changed to generate structure parallel to the photomaterialvelocity.

3. Method

As shown in FIG. 7, a method for patterning of a substrate at sub-micronlength scales using holographic lithography includes moving thesubstrate at sub-micron length scales S110, patterning the substrateusing interference created by EM beams S120, and synchronizing themoving substrate with the interference pattern orthogonal to thesubstrate motion S130. The processes of the method are preferablyperformed simultaneously. The method is preferably implemented inconnection with a system as described above, but any suitable system mayalternatively be used.

Block S110, which includes moving the substrate at sub-micron lengthscales functions to enable continuous patterning of the substrate.Moving the substrate S110 may occur due to actuating of the substratecaused by the chuck. The substrate may be rigidly connected to thechuck, and is thereby actuated by the chuck actuation. Moving of thesubstrate may be translational, rotational, or a combination of the two.Moving of the substrate S110 may alternatively be considered to be inone, two, or three Cartesian dimensions. That is to say translationalmotion along a straight line would be movement in one Cartesiandimension, whereas moving along a circle would be movement along twodimensions in Cartesian dimensions.

Block S120, patterning the substrate using interference created by EMbeams, functions to pattern the substrate. Patterning of the substratemay occur in one to three dimensions. For one dimensional patterning atleast two coherent EM beams may be required, for two-dimensionalpatterning at least three coherent EM beams may be required, and forthree-dimensional patterning at least four EM beams may be required.Since the beams must be coherent to create an interference pattern,patterning may comprise initially of splitting a single beam intomultiple EM beams, adjusting the relative phase of the beams to create apreferred interference pattern, and then generating an interferencepattern upon the substrate by recombining the EM beams.

Splitting a single beam into multiple EM beam functions to createmultiple coherent beams. The closer the wavelength of the “coherent”beams are to one another, the sharper the interference pattern the EMbeams may generate together. Splitting a single beam may occur using abeam splitter. Patterning the substrate S120 in one dimension requiresat least two beams, patterning the substrate in two dimensions requiresat least three beams, and patterning the substrate in three dimensionsrequires at least 4 beams; thus splitting a single beam to create athree-dimensional pattern may require the beam to be split into at least4 beams.

Adjusting the relative phase of the beams with respect to each other iswhat determines the general shape of the interference pattern and isadditionally what is used in synchronizing the moving substrate andmotion-synchronized interference pattern.

Generating an interference pattern functions to create the interferencepattern on the substrate that will be imprinted. One benefit of usingoptical interference to pattern the substrate is that masking of thesubstrate is not required. The constructive and destructive interferenceof the EM beams may automatically accomplish the task.

Generating an interference pattern may preferably generate a periodicpattern, as is typical for an interference pattern. Alternatively orsimultaneously, a gradient pattern may be generated by implementingspatial light phase modulator and/or increasing or decreasing theamplitude of the EM beams. The amplitude may be adjusted by changing thepower output of the EM beam, by adding or removing optical filters,splitting the EM beams, or by some other similar mechanism. More complexmulti-periodic and/or arbitrary patterns may also be generated. Discretebeams may be implemented, where the distance over which the pattern canbe changed is determined by the spot size of the region where the EMbeams interfere. The spot size may then be decreased to make fasterchanges onto the substrate. Alternatively complex multi-periodic andarbitrary patterns may be generated using a Fourier expansion. Spatiallight modulators (arrays of liquid crystals, electro-optic, MEMS, etc.)may be implemented to create and/or modulate beams. Distinct pairs ofbeams would form interference patterns that would contribute to one termof the Fourier expansion. Distinct pairs of beams may even function atdistinct wavelengths, dependent on the substrate material. In addition,multiple exposures or scanning beam exposures may be used for theFourier expansion (or to implement synthetic aperture lithography).Another variation for pattern generation may be an interference patternin conjunction with a mask (contact, projection, or portable conformal).Although a mask may not be necessary for pattern formation, a mask mayaid in creating complex patterns. A grating can be mechanicallyimprinted or made via photolithography or other method at the surface ofthe photomaterial prior to light exposure to create a portable conformalmask (amplitude, phase, or hybrid) that serves as a passive phasecontrol method. In some variations patterns may be generated usingpulsed EM sources that are phase locked to one another. EM beams thatare not completely coherent may be used in variations where sharpcontrasts are not preferred and “smoother”. Alternate methods of patternformation may also be implemented. Additionally, other alternativelithography schemes may be activated/deactivated and can be incorporatedinto the invention (multiple-wavelength, thermal, or other mechanism).

Block S130, synchronizing the moving substrate with the interferencepattern orthogonal to the substrate motion functions to create amotion-synchronized interference pattern that enables continuouspatterning of the substrate. Synchronizing the moving substrate with theinterference pattern S130 may comprise of determining the velocity ofthe substrate, and modulating the EM beams phase difference such thatthe generated phase difference creates a motion-synchronized electricfield, although alternative methods may be implemented. The theory forimplementing the motion-synchronized electric field is preferably thetheory previously described in above in the systems section and may besetup to function actively or passively.

Synchronizing the moving substrate with the interference pattern S130passively includes attaching a fixed mirror to the substrate chuck asper FIG. 4 (or to another object that is motion-synchronized with thesubstrate). The mirror is preferably at least indirectly coupled to thesubstrate (e.g., through the chuck or some other mechanism). Fixing θand ψ as per equations (7, 8) will then synchronize interference patternand the motion and of the substrate. Alternatively instead of mirrors,the chuck, substrate, or some other motion-synchronized object could bereflective and act as a mirror or grating to create additional beams tointerfere in the photomaterial.

Alternatively, synchronizing the moving substrate with the interferencepattern S130 may be done actively as described previously. By modulatingthe phase of a subset of the EM beams, and coupling the modulation tothe substrate motion.

As a person skilled in the art will recognize from the previous detaileddescription and from the figures and claims, modifications and changescan be made to the embodiments of the invention without departing fromthe scope of this invention as defined in the following claims.

1. A system for patterning of a substrate using interference lithographycomprised of: a substrate; a chuck that promotes substrate motion; atleast two EM beams; a beam phase controller, wherein the phasecontroller modifies phases of the EM beams with respect to each othercreating an interference pattern; a displacement sensor that measuresthe substrate displacement; and a feedback control mechanism configuredto monitor and synchronize the substrate motion with the interferencepattern using the beam phase controller and the displacement sensor. 2.The system of claim 1, wherein the substrate motion occurs in NCartesian dimensions and the system comprises of at least N+1 EM beams.3. The system of claim 2, wherein the substrate motion is translational,and the feedback control mechanism synchronizes the interference patternorthogonal to the direction of the translational substrate motion. 4.The system of claim 2, wherein the substrate motion is rotational, andthe feedback control mechanism synchronizes the interference patternorthogonal to the direction of the rotational substrate motion.
 5. Thesystem of claim 1, wherein the substrate is a photosensitive material.6. The system of claim 5, wherein the substrate is reactive to exposureto the interference pattern when incident on the surface therebytransforming to a patterned substrate.
 7. The system of claim 6, furthercomprising a material is filled into a defined patterned void of thepatterned substrate.
 8. The system of claim 1, wherein the feedbackcontrol mechanism is comprised of a mirror rigidly attached to areference frame, as compared to the substrate motion, and the phasecontroller comprises of the spatial distance an EM beam travels fromemitter to substrate, such that the EM interference pattern created bythe EM beam reflected off of the mirror is rigidly coupled at leastindirectly to the substrate and thereby synchronized with the substratemotion.
 9. The system of claim 1, wherein a subset of the EM beams has abeam phase controller controlled by the feedback control mechanism thatadjusts the phases of the subset of the EM beams in accordance to thesubstrate displacement.
 10. The system of claim 9, wherein the beamphase controller further controls the polarization and amplitude of thesubset of the EM beams.
 11. The system of claim 1, wherein substratemotion occurs in three-dimensions, there are six EM beams; the beamphase controller comprises of electro-optic phase modulators for five ofthe EM beams; and the displacement sensor uses interferometry to measuresubstrate displacement.
 12. The system of claim 1, wherein the substrateis a non-solid substrate.
 13. A method for patterning of a substrate atusing interference lithography comprising of: moving the substrate;patterning the substrate using interference created by EM beams; andsynchronizing the moving substrate with the interference patternorthogonal to the substrate motion.
 14. The method of claim 13, whereinpatterning the substrate using interference created by EM beamscomprises of combining at least two coherent EM beams with alteredphases upon the substrate.
 15. The method of claim 14, wherein combiningthe at least two coherent EM beams with altered phases comprises ofinitially splitting an EM beam into multiple beams and altering thephase of a subset of the EM beams prior to the EM beams combining uponthe substrate.
 16. The method of claim 13, wherein the moving substrateis moving in one dimension and at least two EM beams are utilized increating the interference pattern used in patterning the substrate. 17.The method of claim 13, wherein the moving substrate is moving in two ormore Cartesian dimensions and at least two EM beams, per Cartesiandimension, are utilized in creating the interference used in patterningthe substrate.
 18. (canceled)
 19. The method of claim 13, whereinpatterning the substrate comprises of creating a gradient patternincorporating a spatial light phase modulator and by increasing ordecreasing the intensity of the interference pattern.
 20. (canceled) 21.The method of claim 13, wherein synchronizing the moving substrate withthe phase of the EM beam interference pattern orthogonal to thesubstrate motion comprises of fixing a rigid mirror to amotion-synchronized reference frame as compared to the substrate motion,and creating an interference pattern using an EM beam reflected off themirror.
 22. The method of claim 13, wherein synchronizing the movingsubstrate with the phase of the EM beam interference pattern orthogonalto the substrate motion comprises of modulating the phase of a subset ofthe EM beams, and coupling the modulation to the substrate motion.